Final report on carcinogens background document for glass wool fibers. September 9, 2009.

INTRODUCTION: Glass is an amorphous material produced by solidification from a molten state without crystallization and containing a glass former that can be melted and quenched into a glassy state. Silicon dioxide is the major glass former used for commercial applications. Glass wool refers to fine glass fibers forming a mass resembling wool and most commonly used for insulation and filtration. Glass wool fibers were first introduced into commerce in the 1930s and are now among the world's most extensively used insulating materials. Special-purpose fibers make up a small fraction of the synthetic vitreous fibers (SVFs) market and are used, as the name implies, in specialized applications. Glass wool fiber diameters vary within a product but follow an approximately log-normal distribution. The fiber diameter is controlled by the manufacturing process. Fiber diameters vary based on the manufacturing process and the fibers' intended use. The nominal diameter is an estimate of the average fiber diameter of the product. Insulation wool products typically have nominal diameters of 1 to 10 microm and special-purpose fibers have nominal diameters of 0.1 to 3 microm. The diameters of individual fibers in a glass wool product vary widely around the nominal diameter. Unlike crystalline fibers, such as asbestos, glass fibers do not split lengthwise into fibers with smaller diameters, but only break across the fiber resulting in shorter fibers with the same diameter.